Power actuated tools with power adjustment means

ABSTRACT

According to the present invention there is provided an explosively-actuated tool for use in setting fasteners into a substrate, comprising a barrel (2), a driving piston (6) mount within the barrel for driving the fastener into a substrate upon detonation of an explosive charge positioned at or adjacent the rear of the barrel, a firing chamber (8) defined in the barrel rearwardly of the piston, and a system capable of controlling the power of the tool by controlled venting of combustion gases from the firing chamber. The power control system comprises an exhaust port arrangement (14) leading from the firing chamber through the wall of the barrel, and a control member (16) for controlling the effective open area of the exhaust port arrangement. Particularly advantageously, the end of the control rod is provided with a concave arcuate control edge (16b) which provides a relatively uniform relationship between displacement of the control rod and the degree of opening of the exhaust port arrangement. Such a control edge can be formed by a simple chamfer at the end of a cylindrical control rod (16) with the passage also being cylindrical.

BACKGROUND OF THE INVENTION

The present invention relates to power actuated tools for drivingfasteners into a substrate, and more particularly to such tools whichoperate by detonation of an explosive charge.

Power actuated tools for driving fasteners such as nails or pins, into asubstrate such as a concrete or steel beam, conventionally comprise abarrel from which the fastener is expelled by means of a piston drivenby detonation of an explosive charge.

In power actuated tools of this general type, the power output of thetool can be controlled by utilising explosive charges of differentpower. Alternatively a variable power adjustment system may beincorporated into the tool itself. Such power adjustment systems mayoperate by altering the volume of the firing chamber defined in thebarrel of the tool rearwardly of the piston, or by controlled venting ofcombustion gases from the portion of the barrel rearwardly of thepiston. The present invention relates to an improved power adjustmentsystem which operates by providing a controlled venting of thecombustion gases.

SUMMARY OF THE INVENTION

According to the present invention there is provided anexplosively-actuated tool for use in setting fasteners into a substrate,comprising a barrel, a driving piston mounted within the barrel fordriving the fastener into a substrate upon detonation of an explosivecharge positioned at or adjacent the rear of the barrel, a firingchamber defined in the barrel rearwardly of the piston, and means forcontrolling the power of the tool by controlled venting of combustiongases from the firing chamber, said power control means comprising anexhaust port arrangement leading from the firing chamber through thewall of the barrel and a control member for controlling the effectiveopen area of the exhaust port arrangement.

Advantageously, the exhaust port arrangement comprises one or moreradial bores extending through the wall of the barrel. When there aretwo or more such bores, the bores are in axially-spaced arrangementrelative to the barrel.

Advantageously, the exhaust port arrangement opens into an axial bore orother passage within the wall of the barrel, with the control memberbeing defined by a control rod which extends into the passage by anadjustable distance.

Preferably, the control rod extends into the passage from the real endof the passage with the front end of the passage being open fordischarge of the gases from the firing chamber via the exhaust portarrangement. Advantageously, the position of the control rod within thepassage is controlled by a mechanism operative to cause infinite orstepwise movement of the control rod within the passage. Such amechanism may be a screw mechanism.

Particularly advantageously, the end of the control rod is provided witha concave arcuate control edge which provides a relatively uniformrelationship between displacement of the control rod and the degree ofopening of the exhaust port arrangement. Such a control edge can beformed by a simple chamfer at the end of a cylindrical control rod withthe passage also being cylindrical.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 is a schematic sectional view showing the rear end portion of thebarrel of a power actuated tool in accordance with the preferredembodiment of the invention and illustrating in particular a controlmechanism for providing controlled venting of combustion gases from thefiring chamber;

FIG. 2 is an enlarged view similar to FIG. 1 and illustrating in greaterdetail a control rod of the control mechanism and its relationship withthe exhaust port leading from the firing chamber; and

FIGS. 3A to 3C illustrate schematically the progress of the control edgeof the control rod across the array of holes forming the exhaust port.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows part of the barrel 2 of a power actuated tool, the barrel 2being mounted within a main body 4 of the tool for axial movement. Thebarrel 2 houses a fastener driving piston 6. A charge chamber 8 isdefined at the rear end of the barrel 2 for receiving an explosivecharge, and a firing chamber 10 is defined between the rear face 6a ofthe piston 6 and the rear end of the barrel 2. The basic operation ofthe tool is substantially as described in our earlier applications asafore said, with the axial movement of the barrel 2 within the body 4serving to facilitate cocking of the tool when the forward end of thebarrel 2 is pressed against the work surface, and also to reset thepiston 6 within the rear part of the barrel 2 after firing by drawingthe barrel 2 forwardly of the body 4.

The power control system for the tool in accordance with the preferredembodiment of the invention will now be described.

The wall 2a of the barrel 2 around the firing chamber 10 is of anincreased thickness so that its outer diameter closely matches that ofthe inner surface of the body 4. This section of the barrel wall isprovided with an axial through-bore 12 which communicates with thefiring chamber 10 via one, two, or more radial passages 14 spacedaxially along the bore 12, the or each passage 14 collectively definingan exhaust port. A control rod 16 extends into the axial bore 12 throughthe rear end thereof and can be positioned to a variable distance withinthe bore 12 so as to control the effective area of communication betweenthe firing chamber 10 and the axial bore 12 as defined by the open areaof the exhaust port, the cross-section of the rod 16 closely conformingto that of the bore 12. As will be apparent, axial movement of thecontrol rod 16 within the bore 12 will cause the forward end portion 16aof the rod 16 to move across the outer ends of the passages 14 and henceto open or close the passages 14 to a variable extent. The forward endof the bore 12 opens into an annular space 18 defined between the barrel2 and the body 4, and this annular space communicates with a main outletport (not shown) which discharges into the atmosphere. By varying theextent to which the exhaust port defined by the array of passages 14 isopen, by varying the axial position of the control rod 16 within thebore 12, a variable quantity of the gases generated on detonation of theexplosive charge will be exhausted directly from the firing chamber 10thereby varying the effective power of the tool. When the exhaust portis fully closed, the tool will be at maximum power for a given charge,and when the exhaust port is fully open, the tool will be at minimumpower for a given charge. The control rod 16 is capable of infinitelyvariable movement or, alternatively, stepwise movement, between thefully open and fully closed configurations of the exhaust port wherebyto provide a range of intermediate power positions between the maximumand minimum.

The position of the control rod 16 within the bore 12 can be altered byany form of suitable adjustment mechanism. However, as shown, this isachieved by means of a simple screw mechanism comprising a screw 20which is journalled in the body of the tool, and which is rotatable bymeans of a knurled knob 22 which is either located externally of thebody, or which projects through a slot in the body to facilitatemanipulation by an operator. The threaded shank of the screw 22 isengaged in a threaded block 24 carried at the rear end of the controlrod 16. Forwardly of the threaded block 24, the control rod 16 passesthrough an axial bore within a breach block (not shown) which is mountedwithin the body 4 immediately rearwardly of the charge chamber 8. Thebore in the breach block accurately locates the control rod 16 so thatwhen the barrel 2 is moved forwardly relative to the body to reset thepiston 6 after firing, the rear end of the barrel 2 will move forwardlyout of engagement with the control rod 16, and when the barrel 2 isreturned to its rear position its axial bore 12 will align with the endof the control rod 16 and move over the control rod 16. The knob 22 orthe screw 20 may be associated with a detent device to provide a numberof discrete adjustment positions between maximum and minimum. The knob22 may carry suitable markings, or the control rod may be linked to anindicator slide (not shown) so that the power adjustment can easily bedetermined by the operator.

The passages 14 which define the exhaust port can simply be formed byradial holes formed by drill extending between the outside and insidesurfaces of the barrel, with the drillings being axially spaced. This isa much simpler and less expensive process than cutting an elongate slotbetween the firing chamber and axial bore 12 to provide a port which iscapable of selective opening and closure by means of the control rod. Asillustrated, the individual holes are spaced so that a land 14b isformed between adjacent holes. The formation of an exhaust port ofelongate form by means of two or more drilled holes with a landseparating adjacent holes also provides advantages over an exhaust portin the form of an elongate slot in that the presence of the or each landbetween the adjacent holes forms a barrier within the exhaust portitself to unwanted by-pass flow of combustion gas across the peripheralsurface of the rear end of the piston where a seal exists between thepiston and wall of the barrel.

As will be apparent, when the exhaust port is defined by one or moredrilled holes, a control rod of a cylindrical shape at its forward endwill exhibit an essentially transverse "straight" control edge. As thecontrol edge moves across the circular face of each hole and across theland separating adjacent holes, the relationship between displacement ofthe control rod and the degree of opening of the exhaust port is verysignificantly non-linear to the extent that during part of the movementof the control rod where the control edge moves from one hole across theland and onto the adjacent hole, this will not result in any alterationin the effective open area of the exhaust port arrangement. We haveovercome this disadvantage by forming the forward end of the control rod16 with a chamfer 16b whereby the effective control edge of the controlrod as defined at the base of the chamfer and which traverses the outerfaces of the holes 14 is of a concave arcuate form (particularly anelliptical shape) and it is this concave edge which effectively formsthe control edge. This is illustrated schematically in FIGS. 3A to 3Cwhich illustrates the progression of control edge (designated as 16c)across the array of holes 14 when the control rod 16 is moving in adirection indicated by the arrow to close the exhaust port. It is to benoted that while the control edge 16c is moving across the landseparating two adjacent holes 14, it is still acting to progressivelyclose the preceding hole 14 and will still do so when it starts to closethe following hole. It will be appreciated that throughout the range ofmovement of the control rod 16 there will always exist a progressiveopening or closure of the exhaust port without the significant "flatspot" which is present when a control rod with a plain cylindrical endtraverses a land between two adjacent holes. As will also be apparentwith an essentially "straight" transverse control edge provided by aplain cylindrical end of a control rod there will be substantialvariation in the rate of change of opening/closure as it moves acrossthe face of a cylindrical hole, but with a concave arcuate control edgethis rate of change becomes rather more uniform as the control edgemoves across the hole. Accordingly the presence of the arcuate concavecontrol edge provided by the chamfer 16b will lead to a more uniformrelationship between the axial adjustment of the control rod 16 providedby rotation of the screw mechanism and the degree or opening/closure ofthe exhaust port and hence the power control adjustment; this isachieved irrespective of whether there is a single drilling to form theexhaust port or a series of two or more axially-spaced drillings to formthe exhaust port. When the exhaust port consists of two or moredrillings, they may be of the same or different diameters to obtain adesired relationship between control rod position and power output.

The embodiment has been described by way of example only andmodifications are possible within the scope of the invention.

We claim:
 1. An explosively-actuated tool for use in setting fastenersinto a substrate, comprising;a barrel with a longitudinal axis; adriving piston mounted within the barrel for driving the fastener into asubstrate upon detonation of an explosive charge positioned at oradjacent the rear of the barrel; a firing chamber defined in the barrelrearwardly of the piston; and a system for controlling the power of thetool by controlled venting of combustion gases from the firing chamber,the power control system comprising:an exhaust port arrangement leadingfrom the firing chamber and having an effective open area for ventingcombustion gases, and a control member for controlling the effectiveopen area of the exhaust port arrangement, wherein the exhaust portarrangement comprises at least two bores extending radially through thebarrel, the bores leading from the firing chamber into an exhaustpassage extending substantially parallel to the axis of the barrel andthe bores being in axially-spaced arrangement along the axis of thebarrel whereby the adjacent bores are separated by a land and each borehas a radial outer end in communication with the exhaust passage, andwherein the control member is defined by a control rod which extendsinto the exhaust passage by an axially adjustable distance across theradial outer ends of the bores, the control rod having a leading endportion with a concave arcuate control edge operative to provide agenerally uniform relationship between displacement of the control rodand the degree of opening of the exhaust port arrangement as the endportion moves across the radial outer ends of the bores and across theland whereby to achieve progressive opening or closure of the exhaustport arrangement throughout the range of movement of the control rod. 2.The tool according to claim 1, wherein the exhaust passage is defined byan axial bore within the wall of the barrel.
 3. The tool according toclaim 2, wherein the radial bores are drilled through the entire wallthickness of the barrel from the outside of the barrel to the inside ofthe barrel.
 4. The tool according to claim 3, wherein the radial boresare of circular cross-section.
 5. The tool according to claim 1, whereinthe control rod extends into the passage from a rear end of the passage,a front end of the passage being open for discharge of the gases fromthe firing chamber via the exhaust port arrangement.
 6. The toolaccording to claim 5, wherein the position of the control rod within thepassage is controlled by a screw mechanism.
 7. The tool according toclaim 1, wherein the control rod and passage are cylindrical and thecontrol edge is formed by a chamfer at the leading end portion of thecylindrical control rod.
 8. An explosively-actuated tool for use insetting fasteners into a substrate, comprising:a barrel with alongitudinal axis; a driving piston mounted within the barrel fordriving the fastener into a substrate upon detonation of an explosivecharge positioned at or adjacent the rear of the barrel; a firingchamber defined in the barrel rearwardly of the piston; and a system forcontrolling the power of the tool by controlled venting of combustiongases from the firing chamber, the power control system comprising:aplurality of venting passages leading from the firing chamber throughthe barrel to an exhaust passage and through which combustion gases canbe discharged, the passages extending radially relative to the axis ofthe barrel and being in axially spaced relation along the axis of thebarrel whereby a land exists between adjacent passages, and a controlmember movable axially across radial outer ends of the passages tocontrol the effective open area of the passages, the control memberhaving a control edge chamfered to provide a generally uniformrelationship between displacement of the control member and theeffective open area of the passages whereby to provide progressiveincrease or decrease of the effective open area throughout the range ofmovement of the control member unaffected by the presence of the landbetween adjacent passages.